Dispensing Assembly with an Injector Controlled Gas Environment

ABSTRACT

An apparatus for dispensing fusible material onto a surface, wherein the fusible material is in molten form, is provided. The apparatus comprises a dispensing assembly comprising a seal structure. The seal structure controls dispensing of the fusible material. One or more gas injectors are coupled to the dispensing assembly. Each of the one or more gas injectors is adapted to inject at least one gas to the dispensing assembly for controlling a gas environment surrounding at least a portion of the seal structure. An oxidation rate of the fusible material is controlled as a function of at least one characteristic of the at least one gas.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to the concurrently filed U.S. patentapplication identified by attorney docket no. YOR920080076US1, andentitled “Dispensing Assembly With a Controlled Gas Environment,” thedisclosure of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to integrated circuitconnection, and more particularly, to depositing fusible material onto asurface.

BACKGROUND OF THE INVENTION

Using conventional techniques, a silicon chip may be connected to a chipcarrier via a flip chip process which utilizes small solder balls, alsoknown as controlled collapse chip connections (C4s). The chip may thenbe attached to its carrier by a standard solder joining process, or analternative attachment means. The chip carrier then directs the chipsignals and power connections of the silicon chip to bottom side carrierpads. Several technologies have been used to attach the C4 solder ballsto a chip, for example, by evaporation or by electroplating metal ontothe pads of the chip. Recently, a process known as controlled collapsechip connection new process (C4NP) has been proposed. C4NP directlydeposits solder onto a pad by contact transfer. The deposited solderforms C4 solder balls via a thermal reflow process.

C4NP technology has the potential to revolutionize the wafer bumpingindustry by enabling the bumping of many leaded and lead-free solders ina speedy and cost effective manner. For example, the C4NP processfacilitates mass production of solder deposits. This is accomplished byfilling cavities in a glass mold plate with molten solder. Naturally, asthe molten solder is dispensed, it oxidizes rapidly as it is exposed toair. Solder, which usually consists of tin, becomes extremely hard andabrasive when it is oxidized. In many instances, the oxidized solderbuilds up on a fill head seal of the solder dispenser. This buildupdegrades the life of the fill head seal and further results in unwantedsolder residue on the glass mold plate.

SUMMARY OF THE INVENTION

Illustrative embodiments of the present invention beneficially addressthe above-noted problems regarding the oxidation of fusible material andthe buildup of oxidized material on the seal of a dispensing assembly byproviding techniques for controlling a gas environment of the dispensingassembly via one or more gas injectors.

For example, in accordance with one embodiment of the invention, anapparatus for dispensing molten fusible material onto a surface isprovided. The apparatus comprises a dispensing assembly comprising aseal structure. The seal structure controls dispensing of the fusiblematerial. The apparatus further comprises one or more gas injectorscoupled to the dispensing assembly. Each of the one or more gasinjectors is adapted to inject at least one gas to the dispensingassembly for controlling a gas environment surrounding at least aportion of the seal structure. An oxidation rate of the fusible materialis controlled as a function of at least one characteristic of the atleast one gas.

At least one of the one or more gas injectors may comprise a gasmanifold. The gas manifold may be fabricated from a metal, a hightemperature polymer, and/or a ceramic material. At least one of the oneor more gas injectors may comprise at least one gas distribution openingfor providing even gas distribution. Further, at least one of the one ormore gas injectors may comprise a gas reservoir adapted to hold the atleast one gas. At least one of the one or more gas injectors may beoperative to inject the at least one gas at a constant pressure.

Also, the one or more gas injectors may be positioned at a leading edgeof the dispensing assembly and/or positioned at a trailing edge of thedispensing assembly. Each of the one or more gas injectors may beadapted to inject a different gas.

In accordance with a second embodiment of the present invention, amethod for dispensing molten fusible material onto a surface isprovided. At least one gas is injected to a dispensing assembly tocontrol a gas environment surrounding at least a portion of a sealstructure of the dispensing assembly. The dispensing assembly dispensesthe fusible material. Further, an oxidation rate of the fusible materialis controlled as a function of at least one characteristic of the atleast one gas.

In accordance with a third embodiment of the present invention, anapparatus for dispensing molten fusible material onto a surface ispresented. The apparatus comprises: a dispensing assembly with a leadingedge and a trailing edge, comprising: (i) a reservoir for containing thefusible material; (ii) a pressure system coupled to the reservoir forpressurizing the reservoir; (iii) a heating unit surrounding thereservoir for heating the fusible material; and (iv) a seal structurecoupled to the reservoir for controlling a dispensing of the fusiblematerial; a first gas injector comprising a gas reservoir and at leastone gas distribution opening, wherein the first gas injector isoperative to inject a first at least one gas to the dispensing assemblyand is positioned at the leading edge of the dispensing assembly; and asecond gas injector comprising a gas reservoir and at least one gasdistribution opening, wherein the second gas injector is operative toinject a second at least one gas to the dispensing assembly and ispositioned at the trailing edge of the dispensing assembly. At least oneinsulator is positioned between the dispensing assembly and at least oneof the first and second gas injectors.

These and other objects, features, and advantages of the presentinvention will become apparent from the following detailed descriptionof illustrative embodiments thereof, which is to be read in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative cross-sectional diagram depicting an exemplarydispensing assembly comprising a leading edge gas injector and atrailing edge gas injector, in accordance with an embodiment of thepresent invention.

FIG. 2 is an illustrative diagram depicting a bottom view of theexemplary dispensing assembly, in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will be described in conjunction with exemplarymethods and apparatus for dispensing molten solder onto a surface, suchas a glass mold plate. Such methods and apparatus may be used to formsolder balls in a flip chip connection process. It should be understood,however, that the invention is not limited to the particulararrangements and materials as described herein. For example, thetechniques described herein may be applicable to the dispensing of anymolten material that may be susceptible to oxidation or may require acontrolled gas environment. Further, it should be appreciated that theexemplary dispensing apparatus shown in the accompanying figures may notbe drawn to scale, and that modifications to the illustrativeembodiments will become apparent to those skilled in the art given theteachings described herein.

The term “dispensing assembly” as used herein is intended to beconstrued broadly so as to encompass, by way of example and withoutlimitation, any mechanism or apparatus used to dispense any substance.

The term “seal structure” as used herein is intended to be construedbroadly so as to encompass, by way of example and without limitation,any mechanism used to control the dispensing of a substance. Forexample, a seal structure of a solder dispensing assembly preventssolder from leaking outside a target dispensing area.

The term “fusible material” as used herein is intended to be construedbroadly so as to encompass, by way of example and without limitation,any substance which may be used to connect a plurality of surfacestogether. One example of a fusible material commonly used, for instance,in integrated circuit flip chip technology, is solder.

The term “gas injector” as used herein is intended to be construedbroadly so as to encompass, by way of example and without limitation,any mechanism or apparatus that is capable of forcefully dispensing oneor more gases.

Referring initially to FIG. 1, an illustrative cross-sectional diagramdepicts an exemplary dispensing assembly 102 comprising a leading edgegas injector structure 121 and a trailing edge gas injector structure123, in accordance with an embodiment of the present invention.Dispensing assembly 102, which may comprise, for example, a solder fillhead assembly, includes a reservoir 104 containing a molten fusiblematerial 103 (e.g., solder), which is to be dispensed onto a surface.The dispensing assembly 102 may also be equipped with one or moreheating units 106 surrounding the reservoir 104 to heat the containedfusible material 103 so as to maintain the fusible material in moltenform. To assist in high-speed dispensing of the fusible material 103, amechanism to pressurize 108 the reservoir 104 may be coupled to thedispensing assembly 102. The dispensing assembly 102 may furthercomprise a seal structure (e.g., polymer seal), depicted in FIG. 1 asseal portion 110 and seal portion 111 due to the cross-sectionedillustration, at the bottom of the dispensing assembly 102. The sealstructure (110 and 111) surrounds a target dispensing area 112 andprevents unintended leakage of the fusible material 103 outside thetarget dispensing area 112. It is to be appreciated that more than oneseal structure may be used to prevent leakage of the dispensed fusiblematerial. In an illustrative embodiment, the seal structure may beformed as an annular ring surrounding an outlet of the reservoir 104.

The fusible material 103 is dispensed in molten form onto a mold plate114 comprising cavities (e.g., unfilled mold cavities 116 and filledmold cavities 118). This process may proceed as follows. The fusiblematerial 103 contained in the reservoir 104 of the dispensing assembly102 is heated via the one or more heating units 106 surrounding thereservoir 104. The fusible material 103 is heated above its meltingpoint resulting in a phase change to liquid form (e.g., molten form).For instance, tin solder melts at approximately 230° Celsius, in thiscase the heating units 106 heat the reservoir 104 to approximately 250°Celsius.

In practice, the dispensing assembly 102 rests on the mold plate 114 anda nominal load or down force is applied (e.g., 2.5 pounds per linearinch of seal may be applied). The contact between the mold plate 114 andthe seal structure (110 and 111) of the dispensing assembly 102 preventsthe fusible material 103 from leaking uncontrollably out of the bottomof the dispensing assembly 102.

To assist in the dispensing process, the reservoir 104 is preferablypressurized to a pressure between 0 and 20 pounds per square inch (psi).This forces the fusible material 103 to enter the target dispensing area112 and into the unfilled cavities 116 of the mold plate 114. In anillustrative embodiment, the mold plate 114 is moved laterally (e.g.,FIG. 1 illustrates that the mold plate 114 is moving from left to right(115)) underneath the dispensing assembly 102, typically at a speedbetween 0.1 to 10 millimeters per second relative to the dispensingassembly 102, which remains stationary. Alternatively, the dispensingassembly 102 may be moved while the mold plate 114 remains stationary,or the mold plate and dispensing assembly may both be moved in oppositedirections relative to one another. For instance, the dispensingassembly 102 may be operative to move in a direction parallel to asurface (e.g., the mold plate) and/or the dispensing assembly 102 may beoperative to move closer to and/or away from a surface (e.g., the moldplate).

After all the cavities of the mold plate 114 are filled with fusiblematerial 103, the plate is removed and passed to another tool, whichtransfers the molded material to a metalized silicon wafer once thefusible material has cooled to solid form. This second process is knownto a person having ordinary skill in the art and will not be discussedherein.

The exemplary dispensing assembly 102 further comprises one or more gasinjecting structures (e.g., 121 and 123), or gas manifolds, coupled tothe dispensing assembly 102 at a leading edge 120 and a trailing edge122 of the dispensing assembly 102, respectively. The leading edge 120defines the relative direction which the dispensing assembly 102 ismoving toward and the trailing edge 122 is the relative direction inwhich the dispensing assembly 102 is moving away from, relative to themold plate 114. It is to be understood that the assignment of leadingand trailing edges is arbitrary. The gas injector structures (121 and123) function to combat several deficiencies found in conventionalsolder dispensing mechanisms. First, the polymer seals of a conventionalsolder dispensing mechanism tend to degrade quickly when they are heatedto high temperatures (e.g., +250° Celsius) in the presence of oxygen.Second, after a cavity of a mold plate is filled with solder material,atmospheric air instantly oxidizes the dispensed solder resulting in thecreation of an oxidized film over the solder. In some instances, theoxidized film attaches itself to the trailing edge of the solder seal(e.g., seal portion 111). As oxidized material builds up on the seal, iteventually falls off leaving unwanted debris on the mold plate surface.This ultimately results in wafer processing defects.

The lifespan of a seal may be increased and the buildup of oxidizedmaterial may be reduced if the fusible material 103 is dispensed in asubstantially unreactive environment (e.g., devoid of oxidizing agents).The leading edge gas injector structure 121 and the trailing edge gasinjector structure 123 operate to control the gas environment betweenthe seal portion 110 and an outer edge of the leading gas injectorstructure 121 (e.g., region 128) and between the seal portion 111 and anouter edge of the trailing gas injector structure 123 (e.g., region130), respectively. By preventing certain gases from coming in contactwith the dispensed fusible material, one can substantially reduce orprevent oxidation of the fusible material. As a result, the buildup ofoxidized material on the trailing edge of the seal (e.g., seal portion111) may be significantly reduced and the life of the seal structure(110 and 111) may be extended.

Controlling the gas environments of a dispensing assembly may possessadditional benefits. For instance, it should be appreciated that therate at which a fusible material oxidizes and solidifies affects thegrain size, structure, and/or quality of the solidified form of thefusible material. Further, the gas environment in which a fusiblematerial is dispensed may affect adhesion of the fusible material to asurface and the rate at which the fusible material is dispensed.

In an illustrative embodiment, at least one of the one or more gasinjector structures (e.g., 121 and 123) comprises a gas reservoir 125and at least one gas distribution opening 126 (see FIG. 2, 210 and 212for a bottom view). The one or more gas injector structures, or gasmanifolds, may be fabricated from, for example, a metal, a hightemperature polymer, and/or a ceramic material. A gas or a gas mixtureis introduced into a given gas injector structure (not shown) and storedin the gas reservoir 125 therein. The given gas injector structure maythen inject the gas or gas mixture onto the mold plate 114 via the gasdistribution opening(s) 126 positioned along the length of thedispensing assembly 102 (see FIG. 2, 210 and 212).

The gas distribution openings 126 allow for an even and uniformdistribution of gas beneath the dispensing assembly 102 and across themold plate surface 114. Further, introducing the gas or gas mixture intothe gas reservoir 125 prior to injection provides several advantages.For example, the gas reservoir 125 acts as a collection point, whereinthe pressure, temperature, and/or volume of the gas or gas mixture maybe regulated. In one embodiment, the gas or gas mixture is pressurizedwithin the gas reservoir 125 allowing, for example, a rapid andconsistent expulsion of the gas or gas mixture onto the mold platesurface 114 (e.g., regions 128 and 130). Further, temperature regulationof the gas or gas mixture may occur within the gas reservoir 125, whichmay ensure a uniform and consistent gas or gas mixture temperaturebefore the gas or gas mixture is injected onto the mold plate 114 (e.g.,regions 128 and 130). In addition, the volume of the gas reservoir 125may be adjusted, for example, to guarantee that a sufficient volume ofgas or gas mixture is available to adequately flood the mold plate 114(e.g., regions 128 and 130) during operation of the dispensing assembly102.

Preferably, the one or more gas injector structures (e.g., 121 and 123)are thermally isolated from the dispensing assembly 102 so thattemperature fluctuations from the one or more gas injector structures donot affect the temperature of the dispensing assembly 102. In oneembodiment, at least one insulator 124 is placed between the one or moregas injector structures (e.g., 121 and 123) and the dispensing assembly102. The insulator 124 may be made of a low thermal conductivitymaterial such as zirconium oxide ceramic.

Furthermore, the one or more gas injector structures (e.g., 121 and 123)may be mounted to the dispensing assembly 102 in such a way that anythermal expansion of the one or more gas injector structures do notinfluence or mechanically distort the shape of the dispensing assembly102, for example, by pinning one end of the gas injector structure tothe dispensing assembly and attaching the other end to the dispensingassembly via a shoulder screw through a slot.

In an exemplary embodiment, at least one gas is injected beneath thedispensing assembly 102 via the one or more gas injector structures(e.g., 121 and 123). It is to be appreciated that the at least one gasmay be a mixture of gases, rather than one pure gas. Further, the atleast one gas may comprise water vapor. Water vapor may function tocontrol the rate of adhesion of the fusible material 103 to the moldplate 114.

The injected gas or gases flood the area surrounding the solder seal(e.g., 110 and 111) and between the dispensing assembly 102 and the moldplate 114 (e.g., regions 128 and 130). The injected gas or gases thenexit the outer edges of the dispensing assembly 102 (e.g., 127). Itshould be noted that by controlling the gap between the bottom of thegas injector structures (e.g., 121 and 123) and the mold plate 114,and/or by controlling the gas flow rate, the concentration of gasoccupying regions 128 and 130 next to seal portions 110 and 111,respectively, may be controlled. Therefore, each of the one or more gasinjector structures (e.g., 121 and 123) may be operative to move closerto and/or away from the mold plate surface.

The gas introduced at the leading edge 120 need not be the same as thegas introduced at the trailing edge 122. Preferably, a different gas orgas mixture is introduced at the leading edge 120 (e.g., region 128) ofthe dispensing assembly 102 as compared to the trailing edge 122 (e.g.,region 130). As stated above, a polymer seal degrades more rapidly atelevated temperatures in the presence of oxygen. Further, a fusiblematerial is ideally dispensed onto a surface without any oxidation.Therefore, the gas or gas mixture injected at the leading edge 120 ofthe dispensing assembly 102 may be inert and oxygen free. For example,100% nitrogen, argon, helium, etc., may be employed. It may also beadvantageous to consider a lighter than air gas at the leading edge 120of the dispensing assembly 102, because such a gas, for example helium,is easier to expel from the mold plate cavities as fusible material isdispensed, leading to an increased dispensing speed.

As for the trailing edge 122 (e.g., region 130), some oxidation may bepreferred to encourage some solidification of the fusible material;therefore, the trailing edge gas mixture may contain an inert gas with asmall percentage of oxygen mixed in. For instance, in order to form athin oxidized layer on top of the dispensed fusible material, a 94%nitrogen and 6% oxygen gas mixture may be sufficient. In contrast, aircontains 78% nitrogen, 21% oxygen, and ˜1% argon, which causes too muchoxidation. Therefore, by injecting the trailing edge of the dispensingassembly with an oxygen-reduced mixture, oxide buildup on the seal ofthe dispensing assembly (e.g., seal portion 111) is significantlyreduced as compared to an air environment, but a controlled amount ofoxidation will still occur.

To accommodate varying manufacturing circumstances, the gas or gasesinjected at the leading edge 120 and the trailing edge 122 of thedispensing assembly 102 may be adjusted according to the operation stateof the dispensing assembly. For example, when the dispensing assembly isidle (e.g., not performing a dispensing operation), the at least one gasmay be switched to 100% nitrogen to minimize oxidation of standingfusible material. Additionally, depending on a manufacturer'spreferences, the at least one gas may be heated or cooled to promote afaster filling operation or solidification of the fusible material,respectively. For example, to prevent rapid cooling of the fusiblematerial, it may be advantageous to heat the at least one gas injectedat the leading edge 120 (e.g., region 128) of the dispensing assembly102 to warm the mold plate 114 prior to dispensing. In the alternative,the at least one gas may be cooled, thereby cooling the mold plate 114and encouraging rapid solidification of the fusible material; thistechnique may be applied to the trailing edge 122 (e.g., region 130) toquickly cool the filled cavities in the mold plate 114. Furthermore, thespecific composition of the trailing edge gas mixture may be adjusted toinfluence the grain size and/or structure of the fusible material as itsolidifies.

Referring now to FIG. 2, an illustrative diagram depicts a bottom viewof the exemplary dispensing assembly 102 of FIG. 1, in accordance withan embodiment of the present invention. The center portion of thedispensing assembly 201 comprises an opening 202 from which fusiblematerial 103 is dispensed; the fusible material 103 pours directly fromthe reservoir 104 of FIG. 1. The center portion of the dispensingassembly 201 further comprises a circular seal 204 (e.g., polymer seal)surrounding the opening 202, which is equivalent to the seal structure110 and 111 of FIG. 1. It is to be understood that the shape and size ofseal 204 is not limited to that shown. Moreover, seal 204 may be formedas a plurality of separate seal structures.

A leading edge gas injector structure 206 (e.g., leading gas manifold)and a trailing edge gas injector structure 208 (e.g., trailing gasmanifold) are coupled to the center portion of the dispensing assembly201. The center portion of the dispensing assembly 201 is separated fromgas injector structures 206 and 208 by insulating material 205. Theleading edge gas injector structure 206 comprises at least one gasdistribution opening 210 where a first gas or gas mixture is distributedto control the gas environment of the space between a leading portion ofthe seal 204 and an outer edge of the leading edge gas injectorstructure 206 (e.g., region 207). The trailing edge gas injectorstructure 208 comprises at least one gas distribution opening 212 wherea second gas or gas mixture is distributed to control the gasenvironment of the space between a trailing portion of the seal 204 andan outer edge of the trailing edge gas injector structure 208 (e.g.,region 209). The gas injector structures (206 and 208) and the gasdistribution openings (210 and 212) are not limited to any particularnumber, size, and/or shape.

Although illustrative embodiments of the present invention have beendescribed herein with reference to the accompanying figures, it is to beunderstood that the invention is not limited to those preciseembodiments, and that various other changes and modifications may bemade therein by one skilled in the art without departing from the scopeof the claims.

1. An apparatus for dispensing fusible material onto a surface, whereinthe fusible material is in molten form, the apparatus comprising: adispensing assembly comprising a seal structure, wherein the sealstructure controls dispensing of the fusible material; and one or moregas injectors coupled to the dispensing assembly, each of the one ormore gas injectors is adapted to inject at least one gas to thedispensing assembly for controlling a gas environment surrounding atleast a portion of the seal structure, wherein an oxidation rate of thefusible material is controlled as a function of at least onecharacteristic of the at least one gas.
 2. The apparatus of claim 1,wherein the dispensing assembly further comprises a reservoir forcontaining the fusible material.
 3. The apparatus of claim 2, whereinthe reservoir is pressurized.
 4. The apparatus of claim 2, wherein thedispensing assembly further comprises a heating unit surrounding thereservoir for heating the fusible material.
 5. The apparatus of claim 1,wherein the dispensing assembly is operative to at least one of move ina direction parallel to the surface, move closer to the surface, andmove away from the surface.
 6. The apparatus of claim 1, wherein atleast one of the one or more gas injectors comprises a gas manifold. 7.The apparatus of claim 6, wherein the gas manifold is fabricated from atleast one of a metal, a high temperature polymer, and a ceramicmaterial.
 8. The apparatus of claim 1, wherein at least one of the oneor more gas injectors is operative to move closer to and away from thesurface.
 9. The apparatus of claim 1, wherein at least one insulator isplaced between the one or more gas injectors and the dispensingassembly.
 10. The apparatus of claim 1, wherein at least one of the oneor more gas injectors comprises at least one gas distribution openingfor providing even gas distribution.
 11. The apparatus of claim 1,wherein at least one of the one or more gas injectors comprises a gasreservoir adapted to hold the at least one gas.
 12. The apparatus ofclaim 1, wherein at least one of the one or more gas injectors isoperative to inject the at least one gas at a constant pressure.
 13. Theapparatus of claim 1, wherein the one or more gas injectors are at leastone of positioned at a leading edge of the dispensing assembly andpositioned at a trailing edge of the dispensing assembly, wherein eachof the one or more gas injectors is adapted to inject a different gas.14. The apparatus of claim 1, wherein at least one of a dispensing rateof the fusible material and an adhesion of the fusible material to thesurface is controlled as a function of the at least one characteristicof the at least one gas.
 15. The apparatus of claim 1, wherein at leastone of a grain size and a structure of a solidified form of the fusiblematerial is controlled as a function of the at least one characteristicof the at least one gas.
 16. The apparatus of claim 1, wherein the atleast one gas comprises at least one of nitrogen, argon, helium, andoxygen.
 17. The apparatus of claim 1, wherein the at least one gascomprises water vapor, wherein an adhesion of the fusible material iscontrolled as a function of at least one characteristic of the watervapor.
 18. The apparatus of claim 1, wherein at least one of the one ormore gas injectors is operative to control a temperature of the at leastone gas.
 19. A method for dispensing fusible material onto a surface,wherein the fusible material is in molten form, the method comprisingthe step of: injecting at least one gas to a dispensing assembly tocontrol a gas environment surrounding at least a portion of a sealstructure of the dispensing assembly, wherein the dispensing assemblydispenses the fusible material, further wherein an oxidation rate of thefusible material is controlled as a function of at least onecharacteristic of the at least one gas.
 20. The method of claim 19,wherein the at least one gas is injected via one or more gas injectors.21. The method of claim 20, wherein the step of injecting furthercomprises the step of evenly distributing the at least one gas using atleast one gas distribution opening of at least one of the one or moregas injectors.
 22. The method of claim 20, further comprising the stepof storing the at least one gas in a gas reservoir of at least one ofthe one or more gas injectors.
 23. The method of claim 20, wherein theat least one gas is injected at a constant pressure.
 24. The method ofclaim 20, further comprising the step of injecting the at least one gasvia a given one of the one or more gas injectors from at least one of aleading edge of the dispensing assembly and a trailing edge of thedispensing assembly, wherein the given one of the one or more gasinjectors supply a different gas.
 25. An apparatus for dispensingfusible material onto a surface, wherein the fusible material is inmolten form, the apparatus comprising: a dispensing assembly with aleading edge and a trailing edge, comprising: (i) a reservoir forcontaining the fusible material; (ii) a pressure system coupled to thereservoir for pressurizing the reservoir; (iii) a heating unitsurrounding the reservoir for heating the fusible material; and (iv) aseal structure coupled to the reservoir for controlling a dispensing ofthe fusible material; a first gas injector comprising a gas reservoirand at least one gas distribution opening, wherein the first gasinjector is operative to inject a first at least one gas to thedispensing assembly and is positioned at the leading edge of thedispensing assembly; and a second gas injector comprising a gasreservoir and at least one gas distribution opening, wherein the secondgas injector is operative to inject a second at least one gas to thedispensing assembly and is positioned at the trailing edge of thedispensing assembly, wherein at least one insulator is positionedbetween the dispensing assembly and at least one of the first and secondgas injectors.